NCERT Solutions for Class 11 Biology Chapter 6: Anatomy of Flowering Plants

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    1. State the location and function of different types of meristems.

    Ans. Meristems are the cells or groups of cells that have the ability to divide. These cells divide continuously and thus help in increasing the length and thickness of the plant. Based on locations, meristems are of following three types:

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    Types of meristems:

    (a) Apical meristem: It is present at the root and shoot tips of the plant. The divisions in this area facilitate growth and development of root and shoot.

    (b) Intercalary meristem: It is located at the intercalary position and helps to increase the height of the internode. It is generally found in grass, monocots, and pines.

    (c) Lateral meristem: It is located at the lateral side of stems and roots, involved in increasing the thickness of the plant. It includes vascular and cork cambium.

    2. Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.

    Ans. Yes, cork cambium is a type of meristematic tissue that forms the cork.

    It is in particular a lateral meristem, which is concerned with the lateral growth of plants. It is composed of thin-walled rectangular cells and it cuts off cells on both sides. The outer cells differentiate to form cork while the inner cells differentiate into secondary cortex. The cork is impervious to water but allows gaseous
    exchange through the lenticels. Hence, cork cambium forms tissues that form the cork.

    3. Explain the process of secondary growth in the stems of woody angiosperms with the help of schematic diagrams. What is its significance?

    Ans. Secondary growth is the formation of secondary tissues from lateral meristems. It increases the diameter of the stem. In woody plants, secondary tissues constitute the bulk of the plant. They take part in providing protection, support and conduction of water and nutrients. In woody angiosperms, the process occurs as:
    (a) Cambial ring becomes active and starts cutting off new cells from inner and outer sides.
    (b) Cells that are cut off towards the pith mature into secondary xylem.
    (c) Cells that are cut off towards the periphery mature into secondary phloem.
    (d) Cambium is usually more active on the inner side than on the outer side. As a result, a large number of secondary xylem is produced that forms a compact mass.
    (e) Cambial ring forms the major portion during secondary growth in woody stem; the broken epidermal layer is replaced by the activity of cork cambium.
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    Significance: Secondary growth is necessary for growth in girth of the stem. It also provides additional mechanical strength to the stem.

    4. Draw illustrations to bring out the anatomical difference between.

    (a) Monocot root and Dicot root

    (b) Monocot stem and Dicot stem

    Ans. (a) Difference between monocot and dicot root:

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    5. Cut a transverse section of young stem of a plant from your school garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or a dicot stem? Give reasons.

    Ans. A stem is monocot or dicot can be identified by looking at some of its features:
    Dicot stem: It has following unique features:

    (a) The vascular bundles are arranged in the form of a ring, around the centrally-located pith.

    (b) The ground tissue is differentiated into the collenchyma, parenchyma, endodermis, pericycle and pith.

    (c) Medullary rays are present between the vascular bundles.

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    Monocot stem: It has following unique features:
    (a)  Each vascular bundle is surrounded by sclerenchymatous bundle-sheath cells.
    (b) Vascular bundles are scattered.
    (c)  Medullary rays are absent.

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    6. The transverse section of a plant material shows the following anatomical features:

    (a) The vascular bundles are conjoint, scattered and surrounded by a sclerenchymatous bundle sheaths.

    (b) Phloem parenchyma is absent.
    What will you identify it as?

    Ans. Features observed are:
    (a) The vascular bundles are conjoint, scattered and surrounded by a sclerenchymatous bundle sheaths.

    (b) Phloem parenchyma is absent.
    These features are related to monocot stem. So, the plant belongs to monocot.

    7. Why are xylem and phloem called complex tissues?

    Ans. Xylem and phloem are called complex tissues because they are made up of more than one type of cell.

    Xylem components: Tracheids, vessels, xylem parenchyma and xylem sclerenchyma.

    Phloem components: Sieve tubes, companion cells, phloem parenchyma and phloem fibres.

    8. What is stomatal apparatus? Explain the structure of stomata with a labelled diagram.

    Ans. Stomata are small pores present in the epidermis of leaves. They regulate the processes of transpiration and gaseous exchange. The stomatal pore is enclosed between two bean-shaped guard cells. The inner walls of guard cells are thick, while the outer walls are thin. The guard cells are surrounded by subsidiary cells. These are the specialised epidermal cells present around the guard cells. The pores, the guard cells, and the subsidiary cells together constitute the stomatal apparatus.

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    9. Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.

    Ans. The three basic tissue systems in the flowering plants include epidermal tissue system, ground tissue system and vascular tissue system.

    (a) Epidermal tissue system: It forms the outermost covering of the plant body. It consists of tissues like epidermis, stomata, epidermal appendages (trichomes and hairs), etc.

    (b) Ground tissue system: It consists of tissues between the epidermis and vascular bundles. It includes pericycle, cortex, pith and medullary rays.

    (c) Vascular tissue system: The vascular tissue system consists of xylem and phloem that together form vascular bundles.

    10. How is the study of plant anatomy useful to us?

    Ans. The study of plant anatomy useful to us in the following ways:

    (a) It helps us to understand the structural adaptations of plants with respect to diverse environmental conditions.

    (b) It also helps us to distinguish between monocots, dicots and gymnosperms.

    (c) The study of plant anatomy helps us understand plant structure that allows us to predict the strength of wood. This is useful in utilising it to its potential.

    (d) The study of various plant fibres such as jute, flax, etc., helps in their commercial uses.

    11. What is periderm? How does periderm formation take place in the dicot stems?

    Ans. Periderm is the outer covering of certain plants, especially woody plants. It is the outermost layer of the bark made up of cork cells, cork cambium, and phelloderm. It replaces the epidermis of the stems and roots of woody plants.
    Formation in dicot stem:

    (a) A dicot stem continues to increase in thickness due to the activity of vascular cambium.

    (b) The outer cortical and epidermis layers get broken because of pressure from the inner newly formed cells.

    (c) The broken layers are replaced and new protective layers are provided with the help of meristematic tissues lying outside the cortex region of the stem. These meristematic tissues are called cork cambium or phellogen that develops usually in the cortex region.

    (d) Phellogen cuts off cells on both outer and inner sides and towards the outer side.

    (e) The cells differentiate into cork or phellem while towards the inner side, the cells differentiate into the secondary cortex or phelloderm.

    12. Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams.

    Ans. Dorsiventral leaves are found in dicots. The vertical section of a dorsiventral leaf contains three main parts, i.e., epidermis, mesophyll and vascular bundles.

    (a) Epidermis is present on both the upper (adaxial epidermis) and lower (abaxial epidermis) surface. It is covered from outside with a thick cuticle layer.

    (b) Mesophyll tissue is present between the adaxial and abaxial epidermis. It contains the chloroplasts which perform the function of photosynthesis.

    (c) The vascular bundles present in leaves are conjoint and closed. They are surrounded by thick layers of bundle-sheath cells.

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